Choosing the right instrument for environmental sample analysis

Both ICP-OES and ICP-MS are widely used for trace element analysis. Choosing between ICP-OES or ICP-MS depends on the following parameters:

Instrument performance ICP-OES quantitation is based on measurement of excited atoms and ions at the wavelength characteristics for the specific elements being measured. ICP-MS, however, measures an atom’s mass by mass spectrometry (MS). Due to the difference in metal element detection, the lower detection limit for ICP-MS can extend to parts per trillion (ppt), where the lower limit for ICP-OES is parts per billion (ppb). Obviously, if the elements for detection have regulatory limits that are below or near the lower detection limit of ICP-OES, ICP-MS is the instrument of choice.

Characteristics of the environmental sample ICP-OES is mainly used for samples with high total dissolved solids (TDS) or suspended solids and is, therefore, more robust for analyzing ground water, wastewater, soil, and solid waste. It can be used for drinking water analysis as well. But in general, ICP-OES is used to measure contaminants for environmental safety assessment and elements with a higher regulatory limit. ICP-MS, on the other hand, is especially useful for analyzing samples with low regulatory limits. In addition, ICP-OES has much higher tolerance for TDS (up to 30%). ICP-MS has much lower tolerance for TDS (about 0.2%) although there are ways to increase the tolerance. Although both ICP-OES and ICP-MS can be used for high matrix samples, sample dilution is often necessary for use on ICP-MS. In addition, if a sample contains analytes of great difference in concentration, ICP-MS has wider dynamic linear range so the sample may not be diluted to detect these elements at the same time.

Regulatory requirements In the U.S., the regulatory compliance monitoring for ICP-OES is governed by EPA Methods 200.5 and 200.7. EPA Method 200.7 was approved for use as axial view of ICP-OES and is therefore the EPA method for compliance monitoring by ICP-OES. EPA Method 200.8 governs regulatory compliance using ICP-MS. Both EPA 200.7 and 200.8 can be used for compliance of the Safe Drinking Water Act (SDWA) and the Clean Water Act (CWA). For drinking water regulatory compliance or SDWA compliance, either ICP-OES or ICP-MS alone is not sufficient. Regulatory compliance can be accomplished by the combination of ICP-OES (for minerals) and ICP-MS, or ICP-OES and GFAA (using EPA 200.9), or ICP-MS and GFAA (for minerals). ICP-OES cannot be used to measure arsenic, mercury, and some other toxic metals with very low regulatory limits using EPA Method 200.7. ICP-MS can’t be used to measure the minerals (Na, K, Ca, Mg, and Fe) in drinking water using EPA Method 200.8. It is also important to mention that current EPA Method 200.8 version 5.4 cannot use collision cell technology for drinking water analysis, reducing the power to use ICP-MS to minimize polyatomic interferences.